Questions and Answers of Elementary Principles Chemical

A spectrum has a signal-to-noise ratio of 8/1. How many spectra must be averaged to increase the signal-to-noise ratio to 20/1?
Explain why the transmission spectrum in Figure 19-32 is calculated from the quotient (sample transform)/(background transform) instead of the difference (sample transform) - (background
The pathlength of a cell for infrared spectroscopy can be measured by counting interference fringes (ripples in the transmission spectrum). The following spectrum shows 30 interference maxima between
What are the advantages and disadvantages of decreasing monochromator slit width?
What is the role of a filter in a grating monochromator?
Would you use a tungsten or a deuterium lamp as a source of 300-nm radiation? What kind of lamp provides radiation at 4-µm wavelength?
The table shows signal-to-noise ratios recorded in a nuclear magnetic resonance experiment. Construct graphs of (a) signal-tonoise ratio versus n and (b) signal-to-noise ratio versus √n, where n is
Refer to the Fourier transform infrared spectrum in Figure 19-32.(a) The interferogram was sampled at retardation intervals of 1.2660 × 10-4 cm. What is the theoretical wavenumber range (0 to ?) of
Refer to the Fourier transform infrared spectrum in Figure 19-32.(a) The interferogram was sampled at retardation intervals of 1.2660 × 10-4 cm. What is the theoretical wavenumber range (0 to ?) of
The true absorbance of a sample is 1.000, but the monochromator passes 1.0% stray light. Add the light coming through the sample to the stray light to find the apparent transmittance of the sample.
(a) If a diffraction grating has a resolution of 104, is it possible to distinguish two spectral lines with wavelengths of 10.00 and 10.01 µm?(b) With a resolution of 104, how close in wavenumbers
Complex formation by 3-aminopyridine and picric acid in chloroform solution gives a yellow product with an absorbance maximum at 400 nm. Neither starting material absorbs significantly at this
Compound P, which absorbs light at 305 nm, was titrated with X, which does not absorb at this wavelength. The product, PX, also absorbs at 305 nm. Absorbance was measured in a 1.000-cm cell, and the
Compound P, which absorbs light at 305 nm, was titrated with X, which does not absorb at this wavelength. The product, PX, also absorbs at 305 nm. Absorbance was measured in a 1.000-cm cell, and the
The spreadsheet lists molar absorptivities of three dyes and the absorbance of a mixture of the dyes at visible wavelengths.Use the least-squares procedure in Figure 18-3 to find the concentration of
This problem can be worked with Equations 18-6 on a calculator or with the spreadsheet in Figure 18-5. Transferrin is the iron-transport protein found in blood. It has a molecular mass of 81 000 and
Consider a molecule that can fluoresce from the S1 state and phosphoresce from the T1 state. Which is emitted at longer wavelength, fluorescence or phosphorescence? Make a sketch showing absorption,
What is the difference between luminescence and chemiluminescence?
If a sample for spectrophotometric analysis is placed in a 10-cm cell, the absorbance will be 10 times greater than the absorbance in a 1-cm cell. Will the absorbance of the reagent-blank solution
What is the purpose of neocuproine in the serum iron analysis?
What color would you expect to observe for a solution of Fe(ferrozine)43- which has a visible absorbance maximum at 562 nm?
The absorbance of a 2.31 × 10-5 M solution of a compound is 0.822 at a wavelength of 266 nm in a 1.00-cm cell. Calculate the molar absorptivity at 266 nm.
Why is it most accurate to measure absorbances in the range A = 0.3–2?
Why does a compound whose visible absorption maximum is at 480 nm (blue-green) appear to be red?
What is an absorption spectrum?
Explain the difference between transmittance, absorbance, and molar absorptivity. Which one is proportional to concentration?
Fill in the blanks.(a) If you double the frequency of electromagnetic radiation, you __________ the energy.(b) If you double the wavelength, you _________ the energy.(c) If you double the wavenumber,
Semi-xylenol orange is a yellow compound at pH 5.9 but turns red when it reacts with Pb2+. A 2.025-mL sample of semixylenol orange at pH 5.9 was titrated with 7.515 × 10-4 M Pb(NO3)2, with the
Cu+ reacts with neocuproine to form the colored complex (neocuproine)2Cu+, with an absorption maximum at 454 nm. Neocuproine is particularly useful because it reacts with few other metals. The copper
Ammonia can be determined spectrophotometrically by reaction with phenol in the presence of hypochlorite (OCl-):4.37-mg sample of protein was chemically digested to convert its nitrogen into ammonia
(a) A 3.96 × 104 M solution of compound A exhibited an absorbance of 0.624 at 238 nm in a 1.000-cm cuvet; a blank solution containing only solvent had an absorbance of 0.029 at the same wavelength.
(a) What value of absorbance corresponds to 45.0% T?(b) If a 0.010 0 M solution exhibits 45.0% T at some wavelength, what will be the percent transmittance for a 0.020 0 M solution of the same
The cyclic voltammogram of the antibiotic chloramphenicol (abbreviated RNO2) is shown here. The scan was started at 0 V, and potential was swept toward negative voltage. The first cathodic wave, A,
What does a mediator do?
A solution of Sn2+ is to be electrolyzed to reduce the Sn2+ to Sn(s). Calculate the cathode potential (versus S.H.E.) needed to reduce [Sn2+] to 1.0 × 10-8 M if no concentration polarization
In a coulometric Karl Fischer water analysis, 25.00 mL of pure “dry” methanol required 4.23 C to generate enough I2 to react with the residual H2O in the methanol. A suspension of 0.847 6 g of
Consider the cyclic voltammogram of the Co3+ compound Co(B9C2H11)2̅. Suggest a chemical reaction to account for each wave. Are the reactions reversible? How many electrons are involved in each step?
Cd2+ was used as an internal standard in the analysis of Pb2+by square wave polarography. Cd2+ gives a reduction wave at -0.60 (±0.02) V and Pb2+ gives a reduction wave at -0.40 (± 0.02) V. It
Chlorine has been used for decades to disinfect drinking water. An undesirable side effect of this treatment is reaction with organic impurities to create organochlorine compounds, some of which
Ions that react with Ag+ can be determined electrogravimetrically by deposition on a silver working anode:(a) What will be the final mass of a silver anode used to electrolyze 75.00 mL of 0.023 80 M
Calculate the cathode potential (versus S.C.E.) needed to reduce cobalt(II) to 1.0 µM in each of the following solutions. In each case, Co(s) is the product of the reaction.(a) 0.10 M HClO4(b) 0.10
At what cathode potential will Sb(s) deposition commence from 0.010 M SbO+ solution at pH 0.00? Express this potential versus S.H.E. and versus Ag | AgCl.(b) What percentage of 0.10 M Cu2+ could be
A dilute Na2SO4 solution is to be electrolyzed with a pair of smooth Pt electrodes at a current density of 100 A/m2 and a current of 0.100 A. The products are H2(g) and O2(g) at 1.00 bar. Calculate
In which technique, iodimetry or iodometry, is starch indicator not added until just before the end point? Why?
Why is iodine almost always used in a solution containing excess I-?
What is a Jones reductor and what is it used for?
Consider the titration of 25.0 mL of 0.050 0 M Sn2+ with 0.100 M Fe3+ in 1 M HCl to give Fe2+ and Sn4+, using Pt and calomel electrodes.(a) Write a balanced titration reaction.(b) Write two
Compute the titration curve for Demonstration 15-1, in which 400.0 mL of 3.75 mM Fe2+ are titrated with 20.0 mM MnO4- at a fixed pH of 0.00 in 1 M H2SO4. Calculate the potential versus S.C.E. at
Would indigo tetrasulfonate be a suitable redox indicator for the titration of Fe(CN)64- with Tl3+ in 1 M HCl? The potential at the equivalence point must be between the potentials for each
A 20.0-mL solution of 0.005 00 M Sn2+ in 1 M HCl was titrated with 0.020 0 M Ce4+ to give Sn4+ and Ce3+. Calculate the potential (versus S.C.E.) at the following volumes of Ce4+: 0.100, 1.00, 5.00,
What makes a liquid-based ion-selective electrode specific for one analyte?
Which National Institute of Standards and Technology buffer(s) would you use to calibrate an electrode for pH measurements in the range 3–4?
If electrode C in Figure 14-18 were placed in a solution of pH 11.0, what would the pH reading be?Figure 14-18 -1.0 C D -0.5 F G B 0.5 -2 0 2 4 6 8 10 12 14 pH Error, ApH
Convert the following potentials. The Ag | AgCl and calomel reference electrodes are saturated with KCl.(a) 0.523 V versus S.H.E. = ? versus Ag | AgCl(b) -0.111 V versus Ag | AgCl = ? versus
H2S from cigarette smoke was collected by bubbling smoke through aqueous NaOH and measured with a sulfide ion-selective electrode. Standard additions of volume VS containing Na2S at concentration +cS
An ammonia gas-sensing electrode gave the following calibration points when all solutions contained 1 M NaOH.A dry food sample weighing 312.4 mg was digested by the Kjeldahl procedure (Section 10-8)
One glass-membrane sodium ion-selective electrode has a selectivity coefficient . When this electrode was immersed in 1.00 mM NaCl at pH 8.00, a potential of -38 mV (versus S.C.E.) was recorded.(a)
A solid-state fluoride ion-selective electrode responds to F-but not to HF. It also responds to hydroxide ion at high concentration when . Suppose that such an electrode gave a potential of +100 mV
The apparatus in Figure 14-7 was used to monitor the titration of 50.0 mL of 0.100 M AgNO3 with 0.200 M NaBr. Calculate the cell voltage at each volume of NaBr, and sketch the titration curve:
The apparatus in the figure can follow the course of an EDTA titration and was used to generate the curves in Figure 11-10. The heart of the cell is a pool of liquid Hg in contact with the solution
The apparatus in Figure 14-7 was used to monitor the titration of 50.0 mL of 0.100 M AgNO3 with 0.200 M NaBr. Calculate the cell voltage at each volume of NaBr, and sketch the titration curve:
The apparatus in Figure 14-7 was used to monitor the titration of 50.0 mL of 0.100 M AgNO3 with 0.200 M NaBr. Calculate the cell voltage at each volume of NaBr, and sketch the titration curve:
(a) Use the Nernst equation to write the spontaneous chemical reaction that occurs in the cell in Demonstration 13-1.(b) If you use your fingers as a salt bridge in Demonstration 13-1, will your body
What is the difference between E and E° for a redox reaction? Which one runs down to 0 when the complete cell comes to equilibrium?
Which will be the strongest oxidizing agent under standard conditions (that is, all activities = 1): HNO2, Se, UO22+, Cl2, H2SO3, or MnO2?
The basal rate of consumption of O2 by a 70-kg human is about 16 mol of O2 per day. This O2 oxidizes food and is reduced to H2O, providing energy for the organism:(a) To what current (in amperes =
Living cells convert energy derived from sunlight or combustion of food into energy-rich ATP (adenosine triphosphate) molecules. For ATP synthesis, ΔG = +34.5 kJ/mol. This energy is then made
On the basis of the following reaction, state which compound, H2(g) or glucose, is the more powerful reducing agent at pH = 0.00. CO,H СНО НСОН НСОН Eo = -0.45 V НОСН + 2H+ + 2e-
The formation constant for Cu(EDTA)2+ is 6.3 × 1018, and E° is +0.339 V for the reaction From this information, find E for the reaction Cu²+ + 2e Cu(s).
The following cell has a voltage of 0.083 V:Hg(l) | ƒ Hg(NO3)2(0.001 0 M), KI(0.500 M) || S.H.E.From this voltage, calculate the equilibrium constant for the reactionIn 0.5 M KI, virtually all the
Calculate the voltage of the following cell, in which KHP is potassium hydrogen phthalate, the monopotassium salt of phthalic acid. By the reasoning in Figure 13-8, in which direction do electrons
(a) Write a balanced equation for the reaction and calculate E° for the reaction.(b) Predict whether an equimolar mixture of PuO22+ and PuO+2 will oxidize H2O to O2 at a pH of 2.00 and PO2 = 0.20
Calculate the voltage of the cellby considering the following reactions:By the reasoning in Figure 13-8, in which direction do electrons flow?Figure 13-8 Cu(s)|Cu²*(0.030 M)|| K†Ag(CN), (0.010 M),
(a) Using Reactions 2 and 3, calculate E° and write the Nernst equation for the cell.(b) Use the value of Ksp for AgI to compute [Ag+] and find the cell voltage. By the reasoning in Figure 13-8, in
Calculate the voltage of each of the following cells. With the reasoning in Figure 13-8, state the direction of electron flow.(a) Fe(s) | FeBr2(0.010 M) || NaBr(0.050 M) | Br2(l) | Pt(s)(b) Cu(s) |
Calculate E and K for each of the following reactions. (a) I2(s) + 5Br2(aq) + 6H20 = 210, + 10Br + 12H+ (b) Cr2+ + Fe(s) = Fe2+ + Cr(s) (c) Mg(s) + Cl,(g) = Mg²+ + 2C1 (d) 5MNO2(s) + 4H* =
In olden days, mercury cells with the following chemistry were used to power heart pacemakers:What is the cell voltage? If the power required to operate the pacemaker is 0.010 0 W, how many kilograms
A solution containing 0.139 mmol of the triprotic acid tris(2-aminoethyl)amine ∙ 3HCl plus 0.115 mmol HCl in 40 mL of 0.10 M KCl was titrated with 0.490 5 M NaOH to measure acid dissociation
Considering just acid-base chemistry, not ion pairing and not activity coefficients, find the pH and concentrations of species in 1.00 L of solution containing 0.020 mol arginine, 0.030 mol glutamic
Why does the solubility of a salt of a basic anion increase with decreasing pH? Write chemical reactions for the minerals galena (PbS) and cerussite (PbCO3) to explain how acid rain mobilizes traces
Difference plot. A solution containing 3.96 mmol acetic acid plus 0.484 mmol HCI in 200 mL, of 0.10 M KC1 was titrated with 0.490 5 M NaOH to measure K. for acetic acid.(a) Write expressions for the
Difference plot. A solution containing 3.96 mmol acetic acid plus 0.484 mmol HCI in 200 mL, of 0.10 M KC1 was titrated with 0.490 5 M NaOH to measure K. for acetic acid.(a) Write expressions for the
Make a graph of [Ag+], [AgOH(aq)], [CN-], and [HCN] as a function of pH in a saturated solution of AgCN.Consider the following equilibria and do not consider activity coefficients. Find the pH if no
(a) Find the concentrations of species in saturated CaF2 as a function of pH by using Reactions 12-32 through 12-36 and adding the following reaction:Do not include activity coefficients. Produce a
(a) Using the ion-pair equilibrium constant from Appendix J, with activity coefficients = 1, find the concentrations of species in 0.025 M MgSO4. Hydrolysis of the cation and anion near neutral pH is
Include activity coefficients from the Davies equation to find the pH and concentrations of species in the mixture of sodium tartrate, pyridinium chloride, and KOH in Section 12-1. Consider only
(a) Neglecting activity coefficients and ion pairing, find the pH and concentrations of species in 1.00 L of solution containing 0.040 mol 2-aminobenzoic acid (a neutral molecule, HA), 0.020 mol
(a) Neglecting activity coefficients and ion pairing, find the pH and concentrations of species in 1.00 L of solution containing 0.040 mol 2-aminobenzoic acid (a neutral molecule, HA), 0.020 mol
Repeat Exercise 12-A with activity coefficients from the Davies equation.Exercise 12-ANeglecting activity coefficients and ion pairing, find the pH and concentrations of species in 1.00 L of solution
Neglecting activity coefficients and ion pairing, find the pH and concentrations of species in 1.00 L of solution containing 0.010 mol hydroxybenzene (HA), 0.030 mol dimethylamine (B), and 0.015 mol
Give three circumstances in which an EDTA back titration might be necessary.
Pyrocatechol violet (Table 11-3) is to be used as a metal ion indicator in an EDTA titration. The procedure is as follows:1. Add a known excess of EDTA to the unknown metal ion.2. Adjust the pH with
List four methods for detecting the end point of an EDTA titration.
Calcium ion was titrated with EDTA at pH 11, using Calmagite as indicator (Table 11-3). Which is the principal species of Calmagite at pH 11? What color was observed before the equivalence point?
Auxiliary complexing agent. Use the equation derived in Problem 11-19.(a) Prepare a spreadsheet to reproduce the 20-, 50-, and 60-mL points in the EDTA titration of Zn2+ in the presence of NH3 in the
What is the chelate effect?
Iminodiacetic acid forms 2:1 complexes with many metal ions:A 25.0 mL solution containing 0.120 M iminodiacetic acid buffered to pH 7.00 was titrated with 25.0 mL of 0.050 0 M Cu2+.Given that αx2 =
Iminodiacetic acid forms 2:1 complexes with many metal ions:A 25.0 mL solution containing 0.120 M iminodiacetic acid buffered to pH 7.00 was titrated with 25.0 mL of 0.050 0 M Cu2+.Given that αx2 =
A solution containing 20.0 mL of 1.00 × 10-3 M Co2+ in the presence of 0.10 M C2O42- at pH 9.00 was titrated with 1.00 × 10-2M EDTA. Using formation constants from Appendix I for Co(C2O4) and
Suppose that 0.010 0 M Mn2+ is titrated with 0.005 00 M EDTA at pH 7.00.(a) What is the concentration of free Mn2+ at the equivalence point?(b) What is the quotient [H3Y-]/[H2Y2-] in the solution

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